Reactor with end shielding having disk laminations



C. E. MERCIER Oct. 6, 1959 REACTOR wrm END smswmc; HAVING DISKLAMINATIONS Filed Aug. 24, 1956 2 Sheets-Sheet 1 REACTOR WITH ENDSHIELDING HAVING DISK LAMINATIONS Filed Aug. 24. 1956 C. E. MERCIER 1Oct. 6, 1959 2 Sheets-Sheet 2 A 9 x gm {a NMREbRuR d/RAf/VT 729990619P546 70,? (/NAMPS. x10

United States Patent Ofiice 2,907,965 Patented Oct. 6, 1959 END SHIELDING HAVING DISK REACTOR WITH LAMINATIONS Carl Mercier, West Allis, Wis.,assignor to Allis- This invention relates to electric inductionapparatus and more particularly to end shielded current limitingreactors. I

In low voltage industrial power systems, circuit breakers are utilizedfor interrupting the circuits under predetermined operating conditions.Such circuits may have large capacities, and quite often such circuitscan deliver momentary currents beyond the capacity of the circuitbreakers associated with the system. Where the short circuit currentsdelivered may exceed the current interrupting capacity of the circuitbreakers associated with the circuit, either larger capacity breakers(which are expensive and require more space) are substituted or currentlimiting reactors are used in series with the breakers to limit theshort circuit currents to a value within the interrupting capacity ofthebreakers.

Current limiting reactors usually consist of turns of heavy copperhaving an air core. These reactors must be eithermounted in nonmagneticcabinets or provided with magnetic end shielding to limit the stray fluxproduced during normal operation and during prolonged overloads or heavyshort circuit currents, thereby limiting localized heating of thecabinet walls or magnetic. stresses which may cause physical damage tothe cabinet structure.- End shielding also tends to decrease the leakageflux. Heretofore, magnetic shields for current limiting reactors havelacked one or more of the characteristics desirable in such shields.They either failed to provide suflicient shielding to protect associatedcomponents,v with theresult that the unrestrained. magnetic fieldproduced arcing, excessive heating and excessive forces in the metalenclosing cabinet, or they were mechanically too weak. to withstandpressure and impact usually encountered when the shields served as endclamps for holding the coil turns together, or they provided too muchreluctance to satisfactorily direct flux in the desired or chosen path,or they were too difiicult or expensive to manufacture.

In accordance with one aspect of the present invention, a new. andimproved current limiting reactor is provided in which eddy currents arelimited and stray flux is controlled. The reactor comprises thecombination of interconnected layers of conductive windings, spacermembers of insulating material disposed between the layers of conductivewindings, a plurality of slotted metallic disk laminations on theopposite ends of the conductive windings, metal end shields disposedbeyond the opposite ends of the disk larninations, each of the endshields comprising a substantially dish shaped metallic shield slottedin such a manner as to limit the circulation of eddycurrents in theshield, and means for maintaining the protecti-ve end shields incooperative relationship with the stacks ofconductive windings and thedisk laminations.

It is, therefore, one object of the present invention to provide a newand improved reactor for limiting the amount of current in a givencircuit. during: abnormal conditions.

Another object of this invention is to provide a new and improvedreactor having metallic disk laminations and metallic end shields ofparticular geometrical configurations which control the flux paththrough the reactor.

A further object of this invention is to provide a new and improvedcurrent limiting reactor in which metallic disk laminations with aplurality of slots or apertures increase the path length of the eddycurrents induced therein.

A still further object of this invention is to provide a new andimproved current limiting reactor in which slotted metallic disklaminations and slotted metallic end shields limit the circulation ofeddy currents and confine the circulation of stray flux.

Other objects and advantages of, the invention will become apparent fromthe following description when read in connection with the accompanyingdrawings, in which:

Fig. 1 is an elevational view of a reactor embodying features of thepresent invention;

Fig. 2 is an end plan view of the reactor shown in Fig. 1;

Fig. 3 is an end view of the stack of disk laminations shown in Fig. 1illustrating one lamination slot arrangement;

Fig. 4 is an end view of a stack of disk laminations showing amodification of the slot arrangement shown in Fig. 3;

Fig; 5 is an elevational view of a reactor illustrating a modificationof the end bells shown in Fig. 1;

Fig. 6 is-an isometric view partly in cross section of a reactor endshield with parts broken away to show a group of radially arrangedrectangular laminations;

Fig. 7 is an elevational view partly in section of a furthermodification of the reactor shown in Figs. 1 through 6 and embodyingfeatures of this invention; and

Fig. 8 is a current reactance graph of the characteristics of the typeof reactors disclosed.

Referring to the accompanying drawings wherein like reference charactersrefer to like parts throughout, Fig. 1 illustrates a current limitingreactor of the type adaptable for mounting in metal clad switchgear inlow voltage industrial power systems, which can be installed in the mainfeeder bus orin branch circuits to protect a breaker or a group ofbreakers. The current limiting reactor 2 comprises a plurality of layers3, 4, 5, 6, ,7 and 8 of heavy copper conductors, the layers beinginterconnected so as to give a continuous winding, and the ends of thewindings having terminals 9 and 10.

To provide for ventilating and insulating the layers 3, 4, 5, 6, 7 and 8from one another, a plurality of spacer members 11, 12, 13, 14, 15, 16and 17 are associated with these layers. As is more clearly illustratedin Fig. 2, the spacers 11 disposed about the upper surface of layer 3 ofthe conductors are evenly spaced from each other, eight such spacers 11preferably being disposed on one side of the layer 3. The spacers on theopposite sides of and between the other layers forming the reactor 2 aresimilarly disposed so that eifective air spaces or ventilating channelsare provided between the different layers. As is well known in the art,porcelain or some other suitable insulator such as a fibrous materialimpregnated with a resinous binder may be used for these radial spacersseparating each coil layer.

In forming the layers 3, 4, 5, 6, 7 and 8 of the con ductive windings,the different layers are progressively connected so as to provide acontinuous circuit throughout the assembled layers. Suitabletranspositions in the windings may be utilized if so desired.

The invention may be used as a single phase reactor, or in groups asamultiphase reactor. One single phase reactor may be used in each phaseof the circuit, a typical mounting arrangement being three reactorsmounted together for a three phase circuit.

In accordance with the invention claimed, two groups of metallic disklaminations 20 and 21 are provided on opposite ends of the assembledlayers of conductive Windings in the current limiting reactor 2. Thesegroups of laminated disks are substantially identical in constructionand are usually large enough to cover the ends of the conductivewindings of the reactor. The function of the disk laminations is toprovide the desired flux path around the reactor, to provide as short aflux path as possible and to decrease the reluctance of the flux path sothat for equal values of current through a coil a higher reactance isobtained than would be possible without these laminations.

The disk laminations 20and 21 are preferably made of a magnetic materialsuch as steel. The number of laminations may be increased or decreasedaccording to the size and structure of the reactor and the nature of theflux path desired. 'Each lamination is provided with a stud-receivingaperture 23 in its radial center.. A nonmagnetic stud 28 extends throughthe length of the recenter stud. When constructed of a magneticmaterial, they assist the disk laminations in guiding flux in adesirable path. These end shields are constructed similarly to eachother, being approximately a convex section of a sphere. They may beeither of a size to substantially cover the disk laminations, asillustrated in Fig. 5, or of a size to only partially cover the disklaminations, as illustrated in Fig. 1. Since one function of these endshields is to clamp the coil turns together, end shields which have anouter diameter nearly equal to the mean diameter of the reactor coilsdistribute the clamping force fairly evenly between the various coilturns. Holes are provided at the center of end shields 26 and 27 toallow the stud 28 to extend through and cooperate with nuts 31 and 32 tohold the entire assembly together.

End shields 26 and 27 may be provided with a plurality of slots 33spaced about the periphery thereof and extending inwardly therefrom. Theslots in the end shield limit and control the circulation of eddycurrents,

actor and cooperates with a nut at each end of the reactor to hold thewindings, disk laminations and end bells together. The disk laminationsmay be individually insulated with high temperature varnish beforestacking and clamping.

Some or all of the disk laminations may be perforated with a pluralityof spaced slots extending inwardly about the periphery of-thelaminations. These slots may be of any radial length, ordinarily thelonger the slot the more effective its function in reducing circulatingeddy currents and controlling stray flux patterns. The number of slotswill be determined by the size of the current being controlled and thelength of the slots. Slots in the disk laminations tend to increase thepath length of the current induced in the laminations, and thereby toincrease the resistance of the laminations to the eddy current tendingto flow through these laminations. Decreasing the current flowing inthese laminations decreases the counterelectromotive force and permitsleakage flux to shift from an elliptical path which bypasses one stackof laminations, to a path axially through the coil, radially through thedisk laminations and end bell, through the air to the disk laminationsand end bell on the other end, and radially through these disklaminations to the axis of the coil. Further modifications of theslotted construction for disk laminations are illustrated in Figs. 3 and4.

In stacking the slotted disk laminations, the slots may be aligned so asto provide a uniform slot pattern throughout the stack of disklaminations, as illustrated in Fig. 3, or they may be stacked with theslots staggered circumferentially either uniformly or nonuniformly, asillustrated in Fig. 4. As shown in Fig. 3, the laminations of each ofthe groups may be stacked so that corresponding slots in adjacentlaminations of each group form common slots through the group.

If disk lamination slots are staggered, the laminations must beelectrically insulated from each other. Therefore, because of the costof insulation and because of the uncertainties involved, a preferredembodiment of the present invention utilizes vertically aligned slots.If the laminations are stacked so that the slots in adjacent laminationsare aligned, the oxide on the surfaces of these laminations may providethe necessary insulation. The slot patterns in the magnetic disklaminations limit and control circulating eddy currents, and thelaminations provide a low reluctance path for the flux during and afterperiods of short circuit current flow.

Dish shaped metallic end bells, caps or shields 26 and 27 are disposedone outside each of the two stacks of disk laminations 20 and 21, withtheir outer edges bearing thereon. These end shields have a dualfunction, mechanical and electromagnetic. clamp thecoil turns togetherbycooperating with the and the shield provides a low reluctance path forthe. flux. High circulating currents set up in the end shield induce aflux opposed to the main leakage flux. This flux is somewhat reduced byslotting the end shields. Therefore, the radial length and number ofthese end shield v. the laminated disk stacks 20 and 21. In themodification shown, each lamination comprises a plurality of inwardlyextending spaced radial slots 34 disposed about its periphery and aplurality of slots 36 outwardly extending radially from the center ofthe lamination. The group of disk laminations 29 is shown uniformlystacked, so that the slots are vertically aligned throughout each stack.However, these laminations may be so stacked that the slots of onelamination are angularly displaced or staggered with regard to the slotsin adjacent laminations.

In Fig. 4 another modification of the slotted construction of themetallic disk laminations is shown. A plurality of inwardly extendingspaced radial slots 37 is shown about the periphery of each disklamination, with the disk laminations stacked so that the slots are.vertically staggered. This arrangement may come about by random stackingwith no elfort spent to line .up the slots, which makes for a moreeconomical assembly.

In Fig. 5, dish shaped metal end shields 38 are disposed outside of, andsubstantially cover, the stacks of Mechanically, they disk laminations39. These disk laminations and end shields are shown without slotsthereby providing a shorter path length for the current induced in thedisks and end shields, and consequentlyproviding a lower currentreactance than does a structure such as that shown in Fig. 1 withslotted disk laminations and/or slotted end shields. t

Fig. 6 illustrates a further-modification of the invention wherein apartitioned unit -41 comprising a housing 43, magnetic rectangulardividers 44 and filler material 46, replace the combination of the disklaminations and end shield at each end of the' winding shown in Figs. 1,2 and 5. Part of the layer of winding 42 nearest the unit 41 and part ofthe housing 43 of unit 41 are broken away to reveal the spacedrectangular dividers 44 and the fillermaterial 46. The dividers 44 areplane surface members made of a magnetic material such as iron orsteel,-are disposed each on a flat plane, and extend radially relativeto a common point 45, on their edges, to form a plurality ofcomplementary pie shaped sections disposed side by side.

These dividers should preferably be dipped in, or otherwise coated with,a high temperature varnish. The dividers 44 may be secured with anonmagnetic filler material 46, such as high temperature casting resin,nonmetallic spacers, or sand. The housing 43 for the unit may bemetallic or nonmetallic, or may be metallic except for an outernonmagnetic cover 48. A pair of units 41 perform substantially the samefunction as the combination of stacks of disk laminations and endshields shown in Figs. 1, 2 and 5. That is they increase the reactanceof the reactor during periods of short circuit and limit the stray endflux that would otherwise cause excessive heating of the nearby metallicparts and of the cubicle housing.

Fig. 7 shows a further modification of the invention in which a pair ofend caps, each comprising a hollow cylindrical member 51 similar inouter design to those shown in Fig. 6, replace the combination of disklaminations and end shields at each end of the winding shown in Figs. 1,2 and 5. In this design, the members 51 may be formed of metallic ornonmetallic material filled with a magnetic material such as, forexample, grains of iron powder 52. The covers 53 of member 51 maybenonmetallic, with the remainder of the member formed of a metallicmaterial.

Fig. 8 is a graphic comparison of two characteristic curves, current toreactance, illustrating the effect of the presence of radial slots inthe stacks of disk laminations. Curve A is for a reactor of the typeshown in Figs. 1 and 2 but employing unslotted disks, and curve B is forthe same reactor with four equidistantly spaced radial slots in eachstack of disk laminations. As noted from Fig. 8, the ohmic reactance ofthe reactor with radial slots in the disk laminations is higher at highcurrents because of the greater length of the eddy current path, and thegain in reactance is more pronounced when most needed during periods ofhigh current flow or short circuit conditions. a

Although only a few embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

What is claimed is: e

1. ,In a reactor, the combination comprising a stack of interconnectedlayers of electrically conductive windings, spacer members of electricinsulating material disposed between said layers of conductive windings,a plurality of magnetic disk laminations arranged in groups, one groupbeing disposed at each of the opposite ends of said stack with thelaminations of each group being arranged substantially parallel to thelayers of said stack, said groups comprising laminations each havingspaced radially extending slots, end caps disposed one adjacent each ofsaid groups on opposite ends of said stack, each of said end capscomprising metallic material, and means for maintaining said end caps incooperative relation with said stack of conductive windings and saidgroups of disk laminations.

2. In a reactor, the combination comprising a stack of interconnectedlayers of electrically conductive windings, spacer members of electricinsulating material disposed between said layers of conductive windings,a plurality of magnetic disk laminations arranged in groups with eachlamination having equidistantly spaced radially extending slots, onegroup being disposed at each of the opposite ends of said stack with thelaminations of each group being arranged substantially parallel to thelayers of said stack, said laminations of each of said groups beingstacked so [that corresponding slots in adjacent laminations of each ofsaid groups form common slots, end caps disposed one adjacent each ofsaid groups on opposite ends of said stack, each of said end capscomprising metallic material and forming a shield, and means formaintaining said end caps in cooperative relation with said stack ofconductive windings and said groups of disk laminations.

3. In a reactor, the combination comprising a stack of interconnectedlayers of electrically conductive windings, spacer members of electricinsulating material disposed between said layers of conductive windings,a plurality of magnetic disk laminations arranged in groups with eachlamination having spaced radially extending slots, one group of saidplurality of groups being disposed at each of the opposite ends of saidstack with the laminations of each group being arranged substantiallyparallel to the layers of said stack, said laminations of each of saidgroups being stacked so that corresponding slots in adjacent laminationsof each of said groups are staggered, means arranged between adjacentlaminations of each of said groups for electrically insulating saidlaminations from each other, end caps disposed one adjacent each of saidgroups on opposite ends of said stack, each of said end caps comprisingmetallic material forming a shield, and means for maintaining said endcaps in cooperative relation with said stack of conductive windings andsaid groups of disk laminations.

4. In a reactor, the combination comprising a stack of interconnectedlayers of electrically conductive windings, spacer members of electricinsulating material disposed between said layers of conductive windings,a plurality of magnetic disk laminations arranged in groups, one groupbeing disposed at each of the opposite ends of said stack with thelaminations of each group being arranged substantially parallel to thelayers of said stack, said groups comprising laminations each havingspaced radially extending slots, slotted end caps disposed one adjacenteach of said groups On opposite ends of said stack, each of said endcaps comprising metallic material, and means for maintaining said endcaps in cooperative relation with said stack of conductive windings andsaid groups of disk laminations.

References Cited in the file of this patent UNITED STATES PATENTS1,550,889 Doran Aug. 25, 1925 1,747,507 George Feb. 18, 1930 2,605,311Sauer July 29, 1952 2,663,828 Sauer Dec. 22, 1953 OTHER REFERENCESMagazine: Westinghouse Engineer, May 1952, pp. 108-112.

